28 AKT. 2. H. YABE : CRETACEOUS 



might belong to Olcostephanus, while Naumann^^ believed it to 

 be in reality a sjiecimen, foreign to Japan. In the Jimb~> col- 

 lection, however, there is a specimen of Ammonites referable, as 

 the present writer believes, to Olcostephanus, with a label written 

 " Loc. Takambe, a branch of the Ikushumbets river." Thus, 

 at present there is no doubt about the occurrence of the Am- 

 monites of the above named genus in our fauna. 



A specimen described l)y Jimbô"^ as a species of Olco- 

 siephanuSj long ago, is now believed by the present writer to be 

 merely an imperfect specimen of a new species of Scaphites 

 which will be described in some detail in the succeeding part 

 of this memoir. 



OLCOSTEPHANUS UNICUS 3i. 



PI. VI., figs. 5, a, b. 

 Dimensions : — 



Diameter. 4.2 mm. 



Height of the last whorl. 1.9 „ 



Breadth of the last wliorl. 2.3 „ 



Width of umbilicus. 1.2 ,, 



Shell composed of many volutions, inflated. Umbilicus moder- 

 ate in size, deep ; the umbilical wall is perpendicular and its 

 margin rounded. Aperture subcrescentic, broader than high, 

 uniformly rounded on the lateral as well as on the ventral side. 

 Involution rather deep. Surface wdtli numerous transverse ribs ; 

 straight, uniform, narrow l)ut prominent, separated by flat intervals 

 wider than their breadth. The ribs are closely set and nearly 



1) Naumann : Ueber das Vorkommen der Kreidefurmation auf der Insel Jezo. 



2) Jimb5 : I.e. p. n:j (179), pi. IX., figs. .-5, a, b. 



